first peruses is talking with the king about marrying his mother but percy doesn't want that to happen. so the only way it wont is if percy cuts of medusa's head and brings it back to him.
get me medusas head
then he goes to medusa after going to the sisters, hermes and athena they all got percy tools. when percy gets there he uses the tools to kill medusa.
finally percy brings back the head and the king is very surprised he thinks percy is bluffing so the king asks to see it but the king doesn't know that the head can still turn people to stone and then the king turns to stone.